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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        let year=+prompt('请输入年份:')
        if(year%4===0 && year%100!==0 || year%400===0){
            alter('该年为闰年')
        }
        else{
            alter('该年为平年')
        }
    </script>
</body>
</html>